This invention generally relates to the development of images particularly electrophotographic images, and more specifically to the development of images using magnetic toner particles containing quaternary ammonium polymers which materials can be used with or without employing a carrier material that is generally used in most development systems.
The development and formation of images on numerous surfaces such as for example photoconductive materials is well known with the basic xerographic process having been described in Carlson U.S. Pat. No. 2,297,691, this process involving placing a uniform electrostatic charge on a photoconductive insulating layer, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light, and subsequently developing the resultant latent image by depositing thereon a finely divided electroscopic material which is referred to in the art as toner. Generally this toner will be attracted to those areas of the photoconductive layer which retain a charge thus resulting in a toner image that corresponds to the electrostatic latent image. This powder image can then be transferred to a support surface such as paper, and subsequently the transferred image will be permanently affixed to the support surface by a number of known methods including fixing by heat. In these processes it is customary to use developer materials containing a toner and a carrier, one widely used system being described as cascade development which is illustrated for example in U.S. Pat. No. 3,261,855; other systems being magnetic brush development as described in U.S. Pat. No. 2,874,063, and powder cloud development as described in U.S. Pat. No. 2,221,776. In these systems the two component developer is normally employed which includes a carrier and one of the objects of the present invention is to use a toner which does not employ a carrier thereby increasing the efficiency and the quality of the development system.
Use of development systems for magnetic development without employing carrier materials has been suggested for example in Wilson U.S. Pat. No. 2,846,333, which describes the use of magnetic brush system to apply toner particles formed of ferrites and resin materials for developing electrostatic latent images. While this process performs satisfactorily in most environments, the conductivity of the toner resulted in some instances in causing the electrostatic transfer to be somewhat difficult.
Kotz, U.S. Pat. No. 3,909,258, teaches the development of magnetic images without carriers and describes an electrostatic development process employing an inductive magnetic brush without carrier. A toner useful in the magnetic development process of the Kotz patent is described in Nelson U.S. Pat. No. 3,639,245 which teaches a dry toner particle having specific electric conductivity. As indicated the Nelson patent, this type of toner can be prepared by blending magnetite with the resin and subsequently pulverizing the material to a small particle size. These particles are then mixed with conductive carbon black which is embedded in the surface of the particle, and small particles of SiO.sub.2 are mixed into the toner to improve flowability. One of the problems with this type of toner, although it is sufficient for most purposes, is that it does not transfer consistently from a photoconductive substrate to plain bond paper thereby resulting in some instances in image quality of lower resolution than is normally expected.
U.S. Pat. No. 3,970,571 is also of some interest in that it teaches the use of quaternary ammonium compounds as charge control agents and indicates that the charge control agent has been found substantially more effective than the long chain quaternary ammonium surfactant materials which have previously been incorporated in toner compositions.
Accordingly, there is a need for toners, particularly magnetic toners which will be suitable for use in one component magnetic development systems, that is where a carrier is not employed, such toners also being suitable for high speed development and having acceptable electrostatic transfer characteristics for transfer from a photoconductive surface to plain bond paper. Also it is important to have a toner composition that transfers well to paper, for example which will adhere effectively by electrostatic forces in order that image disturbances will avoid blurring when the unfused image is processed prior to fixing.
In copending application U.S. Ser. No. 792,636 filed May 2, 1977 on Single Component Magnetic Toner, the subject matter of this application which is hereby incorporated totally by reference, there is disclosed a coating of magnetic pigments with fatty acid prior to mixing with the resin and spray drying to form a toner which will produce field dependent toner material. However, there continues to be a need for additional field dependent type toners. Also, in copending application, U.S. Ser. No. 854,861, filed on Nov. 25, 1977, which is fully incorporated herein by reference teaches the use of nitrogen containing additives including quaternary ammonium compounds, not polymers, in magnetic toners.